DESCRIPTION (taken from the application) Helicobacter pylori infection is among the most common bacterial infections of man, causing significant morbidity and mortality worldwide. Yet, to date, we do not understand how the organism is transmitted. While most data from the United States, Europe and Australia support direct person-to-person spread, the manner in which this occurs is unknown. We hypothesize that gastric-oral transmission via direct contact with vomitus or aerosolization of vomitus is the most probable means of transmission. We further hypothesize that gastric hypochlorhydria may foster excretion of viable organisms. The specific aims of this study are to evaluate whether viable H. pylori organisms are present in vomitus, air samples obtained during vomiting, saliva and/or feces. To do this, we intend to conduct a clinical experiment in 30 H. pylori infected volunteers. After confirmation of H. pylori infection using serology and 13C urea breath test, subjects will provide saliva and a stool sample for H. pylori testing. One half of these subjects will then be treated with cimetidine for two weeks while the others receive no histamine antagonist. At the end of this period, all subjects will be admitted to the Clinical Research Unit at Stanford where catharsis and emesis will be sequentially induced. Stool, vomit, saliva and air samples will be tested for H. pylori four ways: routine culture, immunomagnetic separation followed by culture, immunomagnetic separation followed by PCR and routine PCR (air filter samples only). The yield of H. pylori from vomitus, air, feces and saliva will be compared. Currently, health interventions related to H. pylori infection involve treatment of H. pylori-related diseases rather than prevention of infection. Availability of prophylactic vaccines remains years to decades away. Understanding the route(s) of H. pylori transmission is a critical starting point for disease prevention and will enable more directed targeting of intervention strategies.